Nested index pages are all promoted to artifact entrypoints

[chubes4]

Problem

ArtifactNormalizer infers role entry for every HTML path ending in index.html, then treats the inferred role as an explicit entrypoint. A normal multi-page artifact therefore marks every nested index document as an entrypoint and MaterializationPlanBuilder maps every page to /.

This surfaced in the production WP Codebox Cloudflare SSI acceptance workload tracked by Automattic/wp-codebox#1975 and Automattic/wp-codebox#2013.

Reproduction

Using automattic/blocks-engine-php-transformer 0.1.15 (5cc48aa0fad87d278d6c9f695c28ad137bf8e1da), compile:

$artifact = array(
	'schema'     => 'blocks-engine/php-transformer/site-artifact/v1',
	'root'       => 'website',
	'entrypoint' => 'website/index.html',
	'files'      => array(
		array( 'path' => 'website/index.html', 'type' => 'text/html', 'content' => '<h1>Home</h1>' ),
		array( 'path' => 'website/api/index.html', 'type' => 'text/html', 'content' => '<h1>API</h1>' ),
	),
);

$result = ( new ArtifactCompiler() )->compile( $artifact )->toArray();
var_export( $result['source_reports']['materialization_plan']['routes'] );

Actual: both routes have source_relation: entrypoint and target_path: /.

Expected: only website/index.html is the entrypoint at /; website/api/index.html is a document with a distinct route.

Root cause

ArtifactNormalizer::role() infers entry for every nested index path. normalize() then promotes any normalized entry role into $safeEntrypoints, losing the distinction between an explicitly declared entry role and an inferred document role.

Acceptance criteria

• An artifact-level entrypoint remains authoritative regardless of file order.
• Nested */index.html documents are not implicitly promoted to additional entrypoints.
• An explicitly declared file role/entrypoint remains supported.
• Multi-page materialization plans produce one root entrypoint and distinct nested document routes.
• Add deterministic regression coverage for file ordering and nested index paths.